A Cu3BHT‐Graphene van der Waals Heterostructure with Strong Interlayer Coupling for Highly Efficient Photoinduced Charge Separation

Two‐dimensional van der Waals heterostructures (2D vdWhs) are of significant interest due to their intriguing physical properties critically defined by the constituent monolayers and their interlayer coupling. Synthetic access to 2D vdWhs based on chemically tunable monolayer organic 2D materials remains challenging. Herein, the fabrication of a novel organic–inorganic bilayer vdWh by combining π‐conjugated 2D coordination polymer (2DCP, i.e., Cu3BHT, BHT = benzenehexathiol) with graphene is reported. Monolayer Cu3BHT with detectable µm2‐scale uniformity and atomic flatness is synthesized using on‐water surface chemistry. A combination of diffraction and imaging techniques enables the determination of the crystal structure of monolayer Cu3BHT with atomic precision. Leveraging the strong interlayer coupling, Cu3BHT‐graphene vdWh exhibits highly efficient photoinduced interlayer charge separation with a net electron transfer efficiency of up to 34% from Cu3BHT to graphene, superior to those of reported bilayer 2D vdWhs and molecular‐graphene vdWhs. This study unveils the potential for developing novel 2DCP‐based vdWhs with intriguing physical properties. Monolayer Cu3BHT with large‐scale uniformity and atomic flatness is synthesized using on‐water surface chemistry, which enables the assembly of novel two‐dimensional van der Waals heterostructure with strong interlayer coupling upon combining with graphene. Employing time‐resolved THz spectroscopy, highly efficient photoinduced net electron transfer from Cu3BHT to graphene with record high efficiency of up to 34% is demonstrated.